Broader effects of modular weld fixtures

Broader effects of modular weld fixtures
The welder must fit the workpiece securely and precisely before laying the bead to ensure dimensional accuracy and to prevent deformation. Most manufacturing jobs specialize in jigs and fixtures, making one-time creations that must be designed by an engineer and milled by a machinist before being used by the welder. Creating custom jigs takes a lot of time in the short term and creates space issues in the long run, as jigs accumulate on the walls and shelves around the work area.
In today’s manufacturing environment, many owners and managers are shifting from the traditional batch and queue approach and towards periodic concepts. Instead of pushing dozens or hundreds of parts down, the JIT operation pulls kits of unequal workpieces into the bottom processes. It helps to reduce or eliminate the most familiar work processes between operations and reduces the overall build time. Result: A component spends more time in line and less time in queue before the next process.
At least it’s ideal. But smaller batch sizes will inevitably require more modification and this will wreak havoc on the high-product-mix shop whose transition times are out of control. This involves a change in the welding cell.
In many cases, it can take three or four weeks or more to build specific welding fixtures, especially if the fixture calls for custom components that the shop cannot machine at home. Engineering, machining and fabrication add to the overall lead-time. And if a customer changes the design of a component, the weld fixture must be replaced with it.

Contract manufacturing stores sell receiving capacity. Suppose the customer changes the design of a part so that it now needs a new blank shape and size, and perhaps even a bending geometry called for a completely different press brake setup. In a matter of minutes, a programmer can insert new parts into the nest for laser cutting. Offline bend simulation and advanced CAD / CAM capabilities significantly reduce press break programming time. But a store is as productive as its barrier process — that is, its barrier. If it takes days or weeks to build a new weld fixture, all the compatibility in the upstream processes will not reduce the cost of a component. Here the modular approach to weld fixing helps.
Components of Modular Fixtures
Modular fixtures include reusable, off-the-shelf components and the manufacturer does not have to create separate fixture elements for each new component. This allows a shop to do a variety of tasks without having to build a separate jig for each task – especially with fewer runs and pattern design. Many components are adjustable and universal.
Modular fixing tables have precision-machined mounting holes to install clamps, supports and other components at any time along with the table top. The mounting holes are set in a one dimensional precision grid pattern for measurement and visual alignment during setup. Hole accuracy is very important to get the modular components in the table.
The mounting holes perform the sequencing and locating function, providing accuracy and repeatability. If the fixture is fitted to a specific hole for a job (for example, if the “three from top and two from left” holes in the grid are indexed), a welder can loosen the component after work, and then reassemble it. Tighten to the same place several hours or weeks after getting the job done.
Modular fixture components include various bars, right angle brackets and large riser blocks. All components are connected to each other using special bolts and have holes and slots for mating with the table. Table and modular fixtures use the same total-grid pattern and hole diameter. Bolts can be simple machine screws or they can be hand-tightened ball locking bolts. Ball locking bolts eliminate the need to reach under the table to tighten parts. Typical parts include V-notch holders for round tubes, high-power magnetic plugs for holding sheet metal, and special plates for holding pipe edges.
Fixing fundamentals do not change as the fixtures are modular. The jigs should stop and identify the workpiece, giving the welder space to work. They should be designed with potential thermal distortion issues in mind and work to minimize those effects. Specific fixture components should also take into account variation in upstream processing – such as spring-stop, which may adapt to the component while keeping components well within tolerance limits.

Figure 2: The setup of modular fixtures consists of many different separate components. Here, the setup has holders for round pipes. It utilizes modular and custom fixing components, including laser-cut plates that support the workpiece. The machine strap clamps are centered so that they do not interfere with the gas metal arc welding gun in the process.
Clamping strategy
Clamping options include special clamps, traditional C or sliding F clamps, toggle clamps or a combination thereof. Which component to use depends on the geometry and volume. Traditional clamps fit well on the sides of a table-top frame or when creating a large, three-dimensional structure. It is very difficult to work them in the middle of the table as the welder needs to be approached to fasten them manually.
Toggle clamps attach to the workpiece in a quick move, further accelerating the tightening. They are compatible with modular fixing tables with adapter plates, which come in the form of predrills or blanks. Disadvantages: Toggle clamps are not as flexible as manual clamps and may require some toggle design for specific functions. Traditional clamps take longer to tighten, but they can be used for a wider range of products.

Suppose a welder works in shifts with a dozen short runs. If he works primarily with fixtures designed with quick-action toggle clamps, he can change fixtures on the modular table in minutes. But since these toggles only work for specific jobs, the shop may need to purchase more toggle clamps to handle the entire product mix. Additionally, the cell next to one welder may require a specific toggle used by another welder. In this case, he will have to go to another job or wait until the adjacent welder finishes his move. Any selected component will interfere with the flow.
Although specific toggles are available, there is still time to swap them between jobs. This may include walking back and forth from the central fixture storage area. All of this takes time and ultimately costs money. In many cases, a combination of toggles and a traditional clamp can work best. Conventional clamps take longer to paste, but they can handle most of the product mix.
Storage factor
Modular fixing tables also contain custom fixtures, creating a hybrid – that is, a fixture that combines both custom and modular components (see Figures 1 and 2). This will speed up the setup for the occasional repetitive task.
Here, another observation of storage. Imagine a welding department that executes several dozen short-term jobs in two shifts. It calls for several dozen fixtures, each of which is placed exactly on its own board or base plate. This may require considerable storage space. In a traditional fixture, 4-by-3-foot welding may require 5 to 4 feet of space in the storage rack.
The modular fixing mechanism changes the storage conditions. Since the holes in the modular fixtures provide an indexing function, a welder can locate the fixture parts in the same place every time a specific job arrives, so the components do not have to be permanently mounted on the board. In the modular setup, the welder disconnects the components from the table after completing the work. He can step by step remove modular components for use with another task and place the remaining task-specific, custom components within 2-1-feet. Can.
CAD effect
How quickly welders install fixtures for the next task is definitely important, but this is not the only factor. Any time a manufacturer works with a fixture it is worth researching and it involves fixture design time. Preparation time may contain only a fraction of the entire order-to-cash cycle: that is, the time between receiving the order and finally shipping and paying for it. A shop engineer can work for days or weeks to design or adjust a fixture and it can cost money in that time.
Most operations may not use CAD for smaller sizes or single-component components. However, CAD takes estimates from the setup for fitters and welders, and CAD’s standard libraries and design procedures speed up the process (see Figure 3). Most modular fixture manufacturers offer downloadable libraries of tooling component models. Saving the setup in the CAD library can also serve as a reference for future setups and is much more complete than improved methods such as taking a photo snapshot of a fixture such as a welder.
When to automate
The declining costs of welding automation and the increasing capabilities of systems and software are not limited to high volume products. More and more businesses are embracing the use of welding robots to address the shortage of skilled welders. That is why fabricators, even those with a high production alloy, continue to follow robotic welding.
In the past most stores would buy robotic systems for a specific high volume job. But what if the contract expires, or the demand level changes? High volume, often ordered job should never be the same. Result: The robotic cell eventually becomes dormant, as it takes a long time to develop fixtures and welding programs for other low-volume work.
Modular fixing systems can help change this situation. Such fixtures on turntables, sky hooks and headstock / tailstock positioners can be integrated into robotic welding cells. The accuracy and repetition capability of the modular fixtures are well matched with the robot. This type of fixing facilitates welding operations involving robots, but still experiences frequent job changes.
Consider a robotically welded job with a modular fixture setup that has two groups of clamps on the same base plate, so that the assembly must first be tightened and welded in one orientation, and then the other group clamps re-oriented. The robot can access the remaining joints. Finally, the part for the remaining joints is sent to the manual welding station.
This contrasts with the traditional idea – the “one-in-one” setup standard. If the robot cannot reach each weld joint, why not tighten this assembly once and weld it manually? Of course, it depends on the job. The design tolerance of a component may require mixing that component as few times as possible. But for other parts, a robot can weld joints faster and more accurately than a person, although the assembly must be reassembled several times.
There is no longer a barrier to efficiency
The advantages of a well-designed modular fixtures system are greater productivity and savings through less lead-times. Engineers need less time and expense for jig design and fabrication. Welders have reduced setup times and increased welding output with more precise and more flexible positions. Organizations respond more actively to design changes and different volume requirements.
Perhaps most importantly, the modular approach makes the fixtures less vulnerable to welding efficiency. Developing fixtures is expensive. That’s the traditional idea, at least. But for proper application, modular fixtures can change the story because it takes less time to design, replace and set up fixtures for the workpiece.